Methods for forming hard images by use of hydrazine derivatives are well known in the art. In particular, methods for forming high contrast images utilizing infectious development with hydrazine derivatives are preferably used for output photographic materials for scanners using laser beams or image setters, because of their good gradation reproducibility, high Dmax and clear dots at edges.
Such image formation methods are described in JP-A-1-179939 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-1-179940, JP-A-6-27571, U.S. Pat. Nos. 4,998,604 and 4,994,365.
A silver halide photographic material generally has a layer in which a hydrophilic colloid such as gelatin is used as a binder, on at least one side of a support. Such a hydrophilic colloidal layer has the disadvantage that it easily expands and contracts according to changes in humidity and temperature.
Changes in the dimension of the photographic materials caused by expansion and contraction of the hydrophilic colloidal layers result in very serious defects for photographic materials for platemaking in which reproduction of halftone dot images or precise line images is required for multicolor print.
In particular, with recent increased high precision in print, a further improvement in dimensional stability of the photographic materials has been intensely desired. Plastic supports of the silver halide photographic materials used in photomechanical processes are generally formed of polyesters represented by polyethylene terephthalate (hereinafter referred to as "PET"). PET films are characterized by excellent dimensional stability, mechanical strength and productivity, and have hitherto been widely used.
However, even when the PET films are used, the required dimensional stability can not be satisfied.
U.S. Pat. No. 3,201,250 discloses a technique in which the ratio of the thickness of hydrophilic colloidal layer(s) to that of a support is specified to obtain a photographic material having less change in dimension, namely excellent in dimensional stability. Further, a technique of adding a polymer latex to a hydrophilic colloidal layer is described in JP-B-39-4272 (the term "JP-B" used herein means an "examined Japanese patent publication"), JP-B-39-17702, JP-B-43-13482, JP-B-45-5331, U.S. Pat. Nos. 2,376,005, 2,763,625, 2,772,166, 2,852,386, 2,853,457, 3,397,988, 3,411,911 and 3,411,912. The evidence of these techniques is described in J. Q. Umberger, Phot. Sci. and Eng., pages 69-73 (1957).
Further, a technique of coating a polyester film support with a vinylidene chloride copolymer is described in U.S. Pat. Nos. 4,645,731, 4,933,267 and 4,954,430. Furthermore, a technique of drying a support at low humidity and subjecting it to heat treatment is described in JP-A-1-229240 and JP-A-1-229244.
However, even when the prior-art techniques for improving dimensional stability are applied to the PET films, they are insufficient for the requirements in high precision print yet.
Syndiotactic styrenic polymer (hereinafter referred to as "SPS") films having a low coefficient of moisture expansion as compared with the PET films are disclosed in JP-A-3-131843. Silver halide photographic materials for photomechanical processes in which the SPS film is used as a support are more improved in register adjustment of a plurality of plates in multicolor print than the photographic materials having the PET film as a support, but they are insufficient for high precision print yet.
When the SPS film is used as the support and the amount of gelatin contained in a photosensitive emulsion layer and other hydrophilic colloidal layers is decreased to intend to improve the dimensional stability, an unexpected problem is encountered in the case of hydrazine high contrast photographic materials.
It is a significant increase in sand-like black spot fog. In particular, when the development time is more prolonged than the standard to thicken halftone dots, which is usually called forced development, or when the amount of sulfites is decreased by deterioration of a developing solution, such a fog is further increased.
It has therefore been intensely desired to provide a silver halide photographic material which exhibits little fog and is excellent in dimensional stability.